Ponding Water on Flat Roof: What To Do

June 3, 2015 Laura MacCormac

If you get a leak due to ponding water that’s been on a flat roof for a few months, don’t blame the ponding water – blame the roof.

water ponding on roof


Quality & Maintenance

A quality roof completely seals out water.  As long as it’s maintained, it will stay sealed and won’t leak.

When a roof is built, it’s designed to prevent water from ponding.  Even flat roofs have a slight slope to them.  The guideline is ¼” per foot, minimum.  The roof should be sloped in a way that guides water towards the drains.  As long as the drains are clear, the water won’t pond.


So why would this happen?

ponding water on roof


Over time buildings settle.  This causes the pitch to change, so the water isn’t all getting to the drain.  When this happens, we build a “cricket” and roof it in, to slope the water to the drain.  Even though a building might not have the best quality roof, we can still help maintain it by preventing water from ponding.

Here’s the cricket.

roof cricket to slope roof

We roof it in with a 2-ply SBS membrane and then cover it with a UV protective coating.

Cricket roofed in.

Clogged Drains

Preventing clogged drains comes with regular roof maintenance.

This is a clogged drain.

Clogged roof drain


This is a drain that has been clogged for too long and is causing a lot of ponding water.

Clogged Drain on Roof

As long as someone is checking those drains every six months, the drains should not have water building up around them.

clean drain

It is inevitable that there will be ponding water on flat roof.  This is why we always recommend a quality roof that can handle some ponding water, so damage is not done between maintenance visits.


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